With the introduction of colorless, directionless, multi-degree ROADM nodes, optical systems are becoming more and more complex and in particular, the number of optical interconnects involved in network elements is growing rapidly. As a result, there is an increasing need to add intelligence to make the deployments of such systems more automated, in particular by having the system software being able to recognize how the different modules and network elements are connected to each other. Another key reason to implement this type of intelligence is to support advanced functions in the optical layer, such as mesh protection and restoration, which require a control plane that has complete knowledge of the optical network topology. Conventional designs that have been proposed to auto-discover optical system topology include 1) using tone signals to trace wavelengths through the network; 2) using a low-level wavelength-tunable monitor signal to probe the system, such as described in commonly assigned U.S. Pat. No. 6,795,607 to Archambault et al. issued on Sep. 21, 2004 and entitled “USE OF TUNABLE LASER FOR OPTICAL PERFORMANCE MONITORING IN WDM SYSTEM,” the contents of which are herein incorporated by reference; and 3) using “smart cables” to automatically detect interconnects between modules.
Limitations of the aforementioned designs include simple tone signals tend to wash out in very long systems. These tone signals also add complexity to transmitter design. A more complex implementation of the tone signals requires fairly high speed modulation on the transmitter side, which is difficult and costly to implement. Further, the use of a tunable probe signal requires a fair amount of additional hardware and software to be added to the system and is not able to monitor connections to individual transceivers, only between line modules. Thirdly, smart optical cables are not widely available, not standardized, and require special hardware for all the connection points. The smart optical cables also only provide information about how modules are physically interconnected within a network element, but not about how wavelengths are being switched or how network elements are interconnected in a mesh network.